[T3] car died on way home

Jim Adney jadney at vwtype3.org
Fri Apr 6 20:11:03 PDT 2012

On 6 Apr 2012 at 19:38, Bryon Garvin wrote:

> Here's the latest.  Got the volt meter out.  Turned key, got 14v out of the
> FI relay under the dash.  Started the car.  Ran fine for 30-40 seconds, 14v
> still coming out of relay... then voltage dropped to zero INSTANTLY.  There
> was no gradual decline in output voltage.  Engine died.  When I did it
> again, same thing happened and I felt the relay click off thru the probe I
> was holding on the terminal.

I agree that this sounds like the fuel pump relay may not be the 
problem. Here's what I would do next. There are 2 wires coming into 
that relay in a white plastic plug. You need to test those wires. 
Attach one of your voltmeter leads to ground and stick the other one 
in the backside of that connector (this is called "backprobing") 
making contact with each wire in turn, as the engine runs and fails.

One wire comes from the main power relay. That should get 14 V as 
soon as the key is turned on and should stay there all the time the 
engine is running. That wire should stay high even after the engine 

The other wire should go high when you turn the key on, but it should 
go low as soon as the engine starts to crank and stay low all the 
time the engine is running. It should stay low for about one second 
after the engine fails, as long as the key stays on.

If you haven't done so already, check that the ground wire under the 
mounting screw for the main FI power relay is tight. You might also 
want to put a finger on that relay while doing your testing. That 
relay should only click off when you turn the key off.

Make sure you know which relay under the back seat is the FI main 
power relay. It's the one with the dedicated red wire coming from the 
battery + terminal.  

Let us know what you find.

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